Cells with adjacent positive and negative electrode strips can be used to provide good high rate discharge performance. Electrode assemblies containing such strips can include one or more pairs of flat, folded or spirally wound positive and negative electrodes. Cells can have housings including containers made from electrically conductive metals that are in electrical contact with one of the electrodes. In such cells the cell container can serve as or provide electrical contact to an external contact terminal.
Electrically conductive leads can be used for making electrical contact between electrodes and another cell component, such as the container or a cover closing a portion of the container. Leads can be in various forms and shapes, such as wires, strips and springs, and leads can be connected to containers or covers in various ways, including by fastening (e.g., welding) and by pressure.
U.S. Patent Application Publication Nos. 2004/0185332, 2005/0238956 and 2006/0147792 relate to electrochemical cells having various configurations for connecting a lead to a negative electrode.
Examples of cells in which an electrode lead is welded to an exposed edge or surface of an electrode current collector are found in U.S. Pat. No. 4,554,227, which is hereby incorporated by reference, and in unexamined Japanese patent publication numbers 05-121064 and 09-035739. In each of these the leads are electrically connected to external terminals by welding. In U.S. Pat. No. 4,554,227 the lead is bent to improve the strength of the welds to the exposed top edge of the electrode current collector.
Examples of cells in which pressure contact is used between a lead and an exposed portion of an electrode current collector at the core of the electrode assembly are found in U.S. Pat. Nos. 3,245,837 and 5,021,306, which are hereby incorporated by reference. In U.S. Pat. No. 3,245,837 the lead is an electrically conductive strip that is fastened to a cover plate and external terminal. In U.S. Pat. No. 5,021,306 the lead is a metal splint, and a leaf spring welded to the cap on the open end of the container makes pressure contact with the splint.
An example of a cell with leads that are bare portions of current collectors protruding from a plurality of electrodes is found in U.S. Patent Publication No. U.S. 2002/0094478 A1, which is hereby incorporated by reference. The plurality of leads is bent and welded together, then fastened to a cell cover. The bends in the leads provide good weld strength.
An example of a cell with a lead extending from the bottom of an electrode assembly and welded to the bottom of the container is found in unexamined Japanese patent publication number 09-330697. A V-shaped groove is formed in a portion of the lead welded to the container to provide good weld strength.
Examples of cells with leads providing electrical contact between one electrode and the cell container and between the other electrode and a cover closing the container are found in U.S. Pat. Nos. 5,418,084 and 4,963,446, which are hereby incorporated by reference, as well as in FIGS. 1 and 2 herein. The cells are cylindrical cells with spirally wound electrode assemblies. As described in further detail below with reference to FIGS. 1 and 2, in each cell a spring provides electrical contact between the positive electrode and the cell cover, and a metal strip lead provides electrical contact between the negative electrode and the sidewall of the container. The spring is fastened to the cell cover and makes pressure contact with the positive electrode current collector exposed at the top of the electrode assembly. The metal strip lead is fastened to the negative electrode and makes pressure contact with the inside surface of the container sidewall. A reliable pressure contact is needed between the lead and the container under normal ranges of variability in manufacturing.
In a cell such as the cell in FIGS. 1 and 2, when made according to the prior art, the lead between the container sidewall and the electrode assembly is held in pressure contact by a tight fit of the electrode assembly in the container. For reliable electrical contact, variability in the inside diameter of the container and the outside diameter of the electrode assembly must be small. One way is to vary the length of a strip of material that is wrapped around the external side surface of the electrode assembly to compensate for variations in thicknesses of the electrodes that can result in differences in diameter. This outer strip of material can be one or more strips of separator or a separate strip of overwrap material, as disclosed in U.S. Pat. No. 4,963,445, which is hereby incorporated by reference.
Metallic lithium and lithium alloys are used as negative electrode active materials in various cell constructions and the lithium is consumed via reaction during cell discharge. In order to maintain conductivity of the negative electrode throughout discharge, various solutions have been presented, including utilizing a higher interfacial theoretical input capacity ratio of the anode to the cathode (A/C), i.e., an overbalance of lithium, theoretical capacity; and utilizing a current collector. Many different types and styles of current collectors have been utilized, see for example U.S. Pat. No. 5,368,958 which discloses a sandwich construction of a lithium sheet, a conductive foil and a second lithium sheet, with the conductive foil positioned between the first and second lithium sheets. Significantly, because the lithium anode is consumed during discharge, having an underbalance of lithium means that the anode may suffer disconnects if there are any dissimilarities in the electrodes. These disconnects prevent transport of electrons across the anode to the appropriate current collector, hence the reason many prior art solutions require collectors to span the length and/or width of the anode.
Current collectors or leads for lithium or lithium alloy negative electrodes have been disclosed that extend lengthwise or widthwise in relation to a strip-like negative electrode that can be folded or rolled into a jellyroll form, for example. U.S. Patent Application Publication No. 2005/0238956 and U.S. Patent Application Publication No. 2006/0172190, both herein fully incorporated by reference, disclose a negative electrode lead extending widthwise, i.e., axially, across a portion of a spirally wound negative electrode about 90% of the width or the axial height of the electrode and positioned near the outer circumference of the wound electrode assembly.